Chronic fatigue syndrome (CFS) is a disease that afflicts people with extreme and debilitating tiredness that lasts for many years and isn’t relieved by rest. Some estimates suggest that it affects up to 1% of the world’s population. We don’t know what causes it. Prostate cancer is one of the most common cancers in the world and kills around 221,000 people every year. Its causes too are largely unknown. What do these two diseases have in common? They have both been recently linked to a virus called XMRV (or xenotropic MulV-related virus in full).

This doesn’t mean that you can ‘catch’ either prostate cancer or CFS. We don’t even know if XMRV actually causes either disease – it could just be that people with weakened immune systems (such as cancer patients or those with CFS) are more easily infected by the virus. For the moment, it’s a fascinating link but one that raises more questions than it answers.

XMRV was first discovered in prostate cancer patients in 2006, and a recent study found XMRV genes in 6% of prostate cancers compared to just 2% of healthy prostates. The virus’s proteins were more starkly linked to cancerous prostates and overall, these tissues were 5 times more likely to carry the virus than their healthy counterparts. Now Vincent Lombardi and Francis Ruscetti have discovered that the XMRV is also over 50 times more common in CFS patients than in the general healthy population.